The Impact of Soft Segment Crystallization and Cross-Link Density on the Shape Memory Performance of the PCL-PTMG/Graphene- Based Polyurethane Nanocomposites

In this research paper, we investigated the impact of soft segment crystallization, the cross-linking density (CLD) and elastic modulus of the synthesized thermoset polyurethanes on their shape memory performance (SMP). A group of tri-block copolymers of poly(epsilon-caprolactone) (PCL) and poly(tetramethylene glycol) (PTMG) with PCLx-PTMG(2000)-PCLx architecture were synthesized and used as polyols in a thermoset polyurethane (PU) structure. Crystallization of the soft segments was controlled through changing PCLx blocks' length. Graphene nanoplatelets, with a fixed content of 0.50 wt.%, was used as the cross-linker and the nano-filler to tune elasticity of the PUs. Analysis of crystallization showed that by increasing PCLx's length from 0 to 2000 D caused a drastic change in the crystallization behavior of the polyols. The polyols used in the thermoset PU nanocomposite led to a wide spectrum of elastic modulus at temperatures close to room temperature. The elastic modulus at room temperature ranged from 20 to 100 MPa. The changes in elastic modulus, CLD and soft segments' crystallization resulted in a complex SMP behavior, which was studied in-detail. The shape recovery rate was also studied, which showed the impact of crystallites' melting, CLD and elastic modulus through a three-stage shape recovery.

Automated summary

In this research paper, the impact of soft segment crystallization, cross-linking density, and elastic modulus on the shape memory performance of synthesized thermoset polyurethanes was investigated. The study found that changing the length of the soft segments affected the crystallization behavior, while the addition of graphene nanoplatelets influenced the elastic modulus. The complex shape memory behavior was analyzed in detail, including the shape recovery rate which was affected by crystallites melting, cross-linking density, and elastic modulus.